Water repellent nonwoven material

ABSTRACT

NONWOVEN LAMINATES COMPRISED OF CELLULOSE WADDING IN A BASIS WEIGHT AMOUNT OF AT LEAST 15 LBS. AND TREATED WITH A WATER REPELLENT HAVE INCREASED WATER REPELLENCY WHEN AT LEAST 9 LBS. OF THE WADDING PRESENT HAVE A LOW POROSITY. THE LAMINATES USUALLY CONTAIN REINFORCING MEANS AND OPTIMUM REPELLENCY IS ACHIEVED WHEN THE LAMINATING ADHESIVE USED PREPARE THE NONWOVENS HAS A LOW SURFACTANT CONTENT.

Sept. 24, 1914 R, v, BRAUN ETAL' 3,837,996-

WATER REPELLENT NONWOVEN MATERIAL Filed March 25. 1970 j INvcNfoRS mmm-l V. BRAUN Auanzv kunnen Hrs.-

United States Patent O 3,837,996 WATER REPELLENT NONWOVEN MATERIAL Ralph V. Braun and Audrey I. Knauer, Neenah, Wis., assignors to Kimberly-Clark Corporation, Neenah, Wis. Filed Mar. 25, 1970, Ser. No. 22,458 Int. Cl. B32b 5/26, 5/12 ILS. Cl. 161--156 6 Claims ABSTRACT F THE DISCLOSURE DESCRIPTION OF THE INVENTION Nonwoven materials are finding increasing use in applications where conventional woven fabrics have heretofore been employed. Such applications include wearing apparel, upholstery, bed sheets, pillow cases, and the like. A particularly desirable feature of nonwovens is their low cost, a factor which allows them to be classified as disposables. As a result, instead of washing or cleaning after use, they are simply discarded.

A particularly useful class of nonwoven materials contain cellulose wadding (e.g., creped tissue) as a primary constituent. The wadding is inexpensive, generally opaque, and has a fabric like hand Thus, fabrics based on such nonwovens are inexpensive and pleasing in appearance and feel. However, since the wadding alone does not have sufficient strength for most applications, it has been the practice to reinforce the wadding with a reinforcing means. Nonwoven reinforcing means are generally used since they are inexpensive and include structures such as scrims (i.e., crossed sets of threads bonded at their points of intersection as described in Hirschy Pat. 2,841,202), drafted webs of staple length fibers such as described in Sokolowski Pat. 3,327,708, carded fiber webs, and webs comprised of a plurality of randomly arranged, substantially continuous thermoplastic filaments such as described in Kinney Pats. 3,341,374 and 3,338,992. In use, the reinforcing webs are laminated between one or more plies of cellulose wadding with an adhesive which does not adversely affect either the appearance or the feel of the wadding itself. Alternatively, the cellulose wadding can constitute the inner portion of the laminate.

With the increased use of nonwoven materials, needs for effectively treating the nonwovens to make them suitable for special applications also arose. `One such need was with respect to rendering the nonwovens water repellent and, thus, more suitable for garment applications and hospital uses such as surgical drape sheets and related items where the material would come into Contact with blood or other fluids. While customary water repellent treatments could be used to impart generally acceptable repellency for some uses, such was not so with respect to those of the materials which were intended for hospital clean room applications. Materials to be used in clean rooms for applications such as surgical gowns, drape sheets, or the like must be subjected to a vigorous sterilization treatment prior to use. Such sterilization treatments involve, for example, exposure to steam at up to 260 F. for as long as one hour or treatment with ethylene oxide gas for eight hours at 140 F. It was soon discovered that customary methods for preparing water repellent nonwovens did not provide adequate products to withstand sterilization procedures with respect to water repellency.

3,837,996 Patented Sept. 24, 1974 In an attempt to improve the water repellent characteristics of nonwoven materials, it was discovered that the adhesive used in laminating the cellulose wadding to the nonwoven reinforcing means, as well as any adhesive used in preparing the reinforcing means itself, was irnportant. Accordingly, materials with improved water repellent characteristics, even after the sterilization procedures, frequently resulted when the adhesive used in preparing the fabric contained less than about 2.5% by weight of water soluble surfactants. |However, success in preparing acceptable material was somewhat haphazard and by no means always assured. Moreover, there was room for substntial improvement even with respect to the material considered acceptable.

Accordingly, it is an object of the present invention to provide a nonwoven material with improved water repellent characteristics comprised of a web of cellulose wadding.

It is a further object to provide such an improved material wherein the good water repellent characteristics remain even after extensive sterilization.

Another object of the invention is to provide a nonwoven material with improved water repellent characteristics and in which the amount of cellulose wadding can be reduced.

A still further object is to provide a water repellent nonwoven material with smaller quantities of repellent than ordinarily employed.

Other objects and advantages of the invention will be apparent from the following detailed description taken in conjunction with the attached drawings in which:

FIG. l is an embodiment of a nonwoven material with sections broken away which can be treated for water repellency in the manner illustrated herein and FIG. 2 illustrates a manner by which the FIG. 1 material can be so treated.

While the invention is susceptible of various modifications and alternative constructions, there is shown in the drawings and will herein be described in detail the preferred embodiments. It is to be understood, however, that it is not intended to limit the invention to the specific forms disclosed. On the contrary, it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

Briefly, the superior water repellent characteristics of the nonwoven materials described herein are achieved by using, as at least one constituent of the nonwoven material, cellulose wadding having a basis weight of at least about 9 lbs., preferably at least 11 lbs., and further characterized by a low porosity. As used herein, low porosity refers to wadding having a Gurley porosity of at least 1 and, preferably, at least 1.5. Gurley porosity is the time (seconds) required to force cc. of air through the wadding using a 5 oz. cylinder and a I; inch orifice. High Gurely values indicate low porosity.

In general single plies of customarily available tissue do not have Gurley porosities high enough for use herein mainly because of the types of forming wires used and the high paper making speeds employed in commercial manufacture. However, as is well known in the paper making art, wadding with low porosity can be obtained by techniques such as using low forming speeds or very ne mesh forming wires. Additionally low porosity can be achieved by employing a furnish with very line fibers or a more thoroughly refined furnish.

Turning now to the drawings, FIG. l illustrates a nonwoven material 10 which can be treated as hereinafter discussed. As shown, the nonwoven material 10 is a laminate comprised of outer plies of creped cellulose wadding 12 and 14 and a single inner ply of a scrim nonwoven reinforcing material 16. The laminate is secured ICC,

by means of adhesive not shown. In the illustrated embodiment, at least one of the plies of cellulose wadding has a basis weight of at least 9 lbs. and a porosity of at least 1 second. As used herein, the term basis weight refers to the dryer basis weight which is the weight of 2880 ft2 of wadding prior to creping.

In nonwoven materials based on cellulose wadding such as illustrated in FIG. 1, the wadding is generally present in several plies with the total basis weight of wadding being at least 15 lbs. and, preferably, at least 20 lbs. Ordinarily, the maximum wadding weight is about 50 lbs. An essential characteristic of the nonwovens described herein is that at least 9 lbs. of the wadding present in the laminate have a Gurley porosity of at least 1 sec. Quite suprisingly, nonwovens containing such a wadding constituent possess unexpectedly superior Water repellent characteristics. While it is preferred that the necessary 9 lbs. of wadding be achieved by the use of a single ply of low porosity wadding having a basis weight of 9 lbs. or higher, individual plies of low basis weight, low porosity wadding can be combined to yield the desired weight.

Referring now to FIG. 2, there is illustrated a manner in which the FIG. 1 material can be treated with a water repellent. As shown, the laminate 10 is impregnated with an aqueous solution 18 of a suitable water repellent by passing the laminate around the roll 22 submerged in the tank 20. After emerging from the tank 20, the laminate, now impregnated with the water repellent, is passed through press rolls 24 and 26 to remove excess repellent and thereafter dried by being passed through the calender stack 28 comprised of heated cans, 30, 32, and 34.

The manner of treatment illustrated in FIG. 2 is quite conventional, and any of the known techniques can be used. More particularly, the repellent contained in the tank 20 is usually present in an amount of about 0.5-10 grams per liter of water, the appropriate amount being based on the particular repellent employed. In order to effect drying, the web speed and the temperature of the drying cans are coordinated so that the web is in Contact with the cans, heated at about 30G-350 F., for about 5-30 seconds.

On a dry solids basis, the repellent is usually present in an amount of about 0.l-2%, based on the weight of the laminate. While increasing the amount of repellent generally increases repellency, the effect may become smaller as larger amounts of repellents are used. Concerning the amount of repellent, less repellent is generally necessary in the presently described nonwovens to achieve a given level of repellency than in products containing high porosity wadding. Moreover, the maximum degree of repellency achievable in the present nonwovens by optimizing factors such as amount of repellent, degree of cure, etc. is greater.

The nature of the Water repellent applied to the nonwovens illustrated herein is not particularly critical. Accordingly, any of the known water repellents can be ernployed, though fluoro chemicals such as those manufactured by the 3M Company and designated as FC-805, FC-808, and 13C-817 have been found to be particularly effective. However, examples of other useful repellents include wax dispersions such as Cravenette N-15, and Impregnole SP and FH and pyridinium repellents such as Cravenette GIQ. Other examples of useful water repellents are given in the American Dyestuff Reporter, 58 (20): 15-19, 45 (Oct. 6, 1969). As indicated previously, the repellent is usually applied as a water solution or dispersion, and, after application, dried. While, with respect to many water repellents, drying under the conditions above recited is adequate to develop their repellency characteristics, it is also frequently desirable to further cure a repellent. Curing at about 350 F.-375 F. for 10-30 seconds is usually sufficient to fully develop repellency properties, though, with respect to some, curing for up to about minutes or more is needed. Curing can also result in economy n water repellent use.

While the reinforcing means illustrated in FIG. 1 is a nonwoven scrim such as prepared in the aforementioned Hirschy patent, any of the other reinforcing means discussed in the opening paragraphs hereof as well as structures such as woven or knitted scrims, oriented threads, split films, and fibrillated plastics are useful as well. The primary requirement of the reinforcing means is that it sufficiently reinforce the creped cellulose wadding for the particular end use application without adversely affecting the materials hand In addition, the reinforcing means should not be prepared from a material which adversely affects water repellency nor should its manner of prepara- Ation (e.g., the adhesives used) have such an affect. Particularly useful materials for nonwoven reinforcing means include nylon and/or glass fibers when scrims are used, rayon fibers when drafted webs are employed, rayon or cotton fibers when carded webs are used, and synthetic polymers, such as polypropylene, for the continuous filament webs.

In addition to the independent reinforcing means illustrated above, the wadding itself can be reinforced such as by including long fibers in its preparation. Thus, laminates of only several wadding plies wherein at least one of the plies has a basis weight and porosity as above described will exhibit superior water repellent characteristics when treated as herein illustrated. Such laminates are particularly useful in applications where high strength is not required.

As has been emphasized, the repellent characteristics of the nonwoven materials are dependent on the adhesive used in laminating the reinforcing means to the cellulose web. Such is also true with respect to the adhesive, if any, used in preparing the reinforcing means. However, since it is generally true that greater quantities of adhesive are used in laminating than in bonding the reinforcing means itself, the necessity of having a low surfactant level is most important with respect to the laminating adhesive. Surfactant level in the adhesive can be easily determined by means of a 3 hour Soxhlet extraction with an alcoholwater (-20) solution. Surfactant levels of less than about 2.5 weight percent, and, preferably, less than about 1 weight percent, are desirable. Just as presence of excessive amounts of surface active agents in the adhesive is detrimental to water repellency, the presence of certain surface active agents, such as sodium lauryl sulfate, in the tissue can also produce similar results.

Useful laminating adhesives are plastisols comprising low surfactant polyvinyl chloride resins in plasticizers such as dioctyl phthalate. Examples of such resins having a low surfactant content are those sold under the names Geon 128, Opalon 440 and Union Carbides resins QYOH-2 and VLFV. The laminating adhesive is ordinarily used in an amount of about 5-15 grams per yd.2, and should be applied in a manner such that the fiexibility of the resulting laminate is not adversely affected. Accordingly, with a scrirn such as illustrated in FIG. 1, the adhesive can be directly applied to the threads forming the scrim over their total surface. On the other hand, when a reinforcing means such as a drafted fiber web is employed, the laminating adhesive should be applied in a. spaced pattern so as to preserve the flexibility of the structure.

The following examples illustrate the present invention. All parts and percentages are by weight unless otherwise indicated. In evaluating the water repellency of the illustrated nonwoven materials, the following test was employed: 600 ml. of a normal saline solution are added to a one quart mason jar. A sample of the nonwoven material to be tested is then placed over the mouth of the jar and the open ring screwed down on the jar tightly. The jar is then inverted on a glass plate located a few inches above a mirror. The repellency of the nonwoven material is measured as the time required for the first liquid water to penetrate the nonwoven material and wet the glass plate. It is desirable that the laminate resist penetration for at least 30 minutes and, preferably, for at least 90 minutes.

In the examples, scrim reinforced nonwoven materials such as illustrated in FIG. l were employed. A nylon scrim having 30 denier laments in the Warp direction spaced 12 to the inch and 70 denier filaments in the ll direction spaced 5 to the inch was used. The scrim was bonded with a polyvinyl acetate adhesive. Lamination of the scrim to the creped cellulose wadding plies was accomplished with low surfactant Geon 128 plastosol adhesive which was applied to each side of the scrim in an amount of -12 grams per yard.2. After preparation of the nonwoven materials, the materials were treated with 3M Companys Water repellent 13C-808 to a solids add on of about 0.2% and, thereafter, dried over 300 F. cans for 20-25 secs. Table l illustrates the results of repellency measurements obtained on nonwoven materials containing the indicated plies of cellulose wadding.

TABLE 1 Wedding plies Gurley porosity Repelof lamleney Example Top 1 side Bottom side inate (min.)

1 2 plies of ordinary 1 ply of 9 lb. 2. 3 53 high porosity tissue, 1.3 7.7 lb. tissue. sec. porosity. 2 .do 1 ply of 11 lb. 3.1 83

tissue, 1.8 sec. porosity. 3 do 1 ply of 13 lb. 3. 5 2 120 tissue, 2.1 sec. porosity. 4 1 ply of low 1 ply of 11 lb 4. 3 3 120 porosity 11 lb. tissue, 1.8 soc. tissue. porosity. Comparative. 2 plies of ordinary 2 plies oi ordi- 2. 3 7

high porosity nary 7.7 lb. 7.7 lb. tissue, tissue, 0.7 sec. 0.7 sec. porosity. porosity.

1 Side in contact with glass plare.

2 Test stopped after 120 min.

As is evident from Table l, the nonwoven materials of the present invention have unexpectedly good water repellency. Moreover, the repellency is not adversely affected by sterilization and, in fact improves somewhat due to the curing effect of sterilization on the repellent. In addition, by comparison between the Example l material and the Comparative material, it can be seen that replacing two plies of conventional material with a single ply of low porosity wadding having a basis weight of 9 lbs. results in a substantial increase in Water repellency. Such improvement occurs even though the total amount of cellulose wadding in the material is reduced from about 30 lbs. to about 24 lbs. Moreover, as illustrated by Examples 2-4, even greater improvements in repellency can be achieved by using higher weight low porosity tissue, especially when such tissue is employed throughout the nonwoven material.

Thus, it is apparent that there has been provided according to the invention, a nonwoven material which satisfies the aims, objectives, and advantages as set forth above.

We claim as our invention:

1. In a water repellent laminate comprising cellulose wadding in a basis weight amount of 20-50 lbs. and employing a laminating adhesive containing a low level of surfactant, said laminate having been treated with a water repellent and in a manner to develop the repellency characteristics thereof; the improvements wherein at least one ply of cellulose wedding having a Gurley porosity of at least 1.5 seconds is used in preparing said laminate and wherein cellulose wadding having a Gurley porosity of at least 1.5 seconds is present in a basis weight amount of at least 9 lbs.

2. In the laminate of claim 1 the improvement wherein cellulose wadding having a Gurley porosity of at least 1.5 seconds is present in a basis weight amount of at least 11 lbs.

3. In a nonwoven material comprising cellulose wadding in a basis weight amount of 20-50 lbs. laminated t0 a reinforcing means with an adhesive containing a low level of surfactant, said material having been treated with a water repellent and in a manner to develop the repellency characteristics thereof; the improvements wherein at least one ply of cellulose wadding having a Gurley porosity of at least 1.5 seconds is used in preparing said laminate and wherein cellulose wadding having a Gurley porosity of at least 1.5 seconds is present in a basis weight amount of at least 9 lbs.

4. The nonwoven material of claim 3 wherein at least one ply of cellulose wadding is on either side of the reinforcing means and wherein at least one ply of cellulose wadding'is present which has a basis weight of at least 9 lbs. and a Gurley porosity of at least 1.5 seconds.

5. The nonwoven material of claim 4 wherein at least one ply of cellulose wadding is present which has a basis weight of at least 11 lbs. and a Gurley porosity of at least 1.5 seconds.

6. The nonwoven material of claim 5 wherein the reinforcing means is a non-woven scrim.

References Cited UNITED STATES PATENTS 2,902,395 9/1959 Hirschy et al l6l--143 X 2,673,824 3/1954 Biefeld et al 161-156X 3,047,444 7/1962 Harwood 161-156 X 2,774,127 12/1956 Secrist 161-156 X 3,081,517 3/1963 Driesch 161--156 2,684,314 7/1954 Ross 161-156 X CHARLES VAN HORN, Primary Examiner R. A. DAWSON, Assistant Examiner U.S. Cl. X.R. 161-82, 89, 143 

